The more recently developed sources of light energy such as semiconductor junction lasers and light emitting diodes, for example, have found wide acceptance in use with integrated and fiber optics systems. However, in order to avail of the more desirable advantages of the advances incorporated in the technology of such recently developed sources of light energy, a means must be devised for efficiently coupling light emitted from the source into the receiving element such as a fiber optic transmission line, for example.
In the case of light sources such as semiconductor junction lasers and light emitting diodes, the emitting surface area is extremely small and as a consequence any device for coupling the emitted light energy out of the source and into the receiving element must be of commensurately small geometry. One means of accomplishing the desired coupling is through the use of extremely small miniature lenses of appropriate configuration. In the prior art the use of epoxy and arsenic/selenium glass lenses for coupling light energy out of light emitting diodes has been known and practiced for a considerable time.
For performing the coupling function efficiently it has been generally appreciated that if the material employed in the coupling lens has a refractive index which closely matches the refractive index of the emitting source of light energy, the efficient transfer of such energy will be maximized. For example, in a typical instance where light energy is coupled from a junction laser element into a fiber optic transmission line, the ideal lens for performing the coupling function will have a cylindrical configuration in terms of optical characteristics and a refractive index substantially matching the refractive index of the lasing material which may typically be of the order N=3.5.
Non-conventional lens materials such as arsenic-selenium glass, for example, may be selected to provide the substantially matching index of refraction. However, the extremely small emitting surface area of a light energy source such as a light emitting diode (typically of the order of only one to several microns) makes the use of a conventional lens employing cylindrically configured surfaces, for instance, most difficult. Such conventional cylindrical lenses, would necessarily have an extremely small geometry defined by maximum dimensions of approximately no more than 10 to 100 microns, for example, and consequently conventional optical lens fabrication by the use of customary grinding and polishing techniques to generate the required curvatures of surfaces is thus rendered extremely difficult in any case, and virtually impossible in many cases.